Mosquitoes infect humans with malaria, but we give it back too

Research reported this week in Nature Communications provides detailed data on the importance that different age groups have on malaria transmission, as well as suggesting new sensitive diagnostics measures that might reduce transmission.

Infectious reservoir

When a mosquito feeds on a person with malaria, the malaria parasite can be transmitted to the mosquito. This contributes to malaria transmission and is known as the infectious reservoir. Understanding this interaction could be influential in improving malaria control strategies.

Collaborators from the London School of Hygiene & Tropical Medicine (LSHTM) and Radboud University Medical Center (RUMC) in Nijmegen, The Netherlands and research institutions in Kenya and Burkina Faso, performed large scale assessments of human infectivity to mosquitoes, in areas with different levels of malaria transmission. To establish whether individuals were infective or not, mosquitoes were allowed to feed on human blood through membranes and the mosquitoes were later assessed for the presence of parasites.

More than a thousand individuals were tested and results showed that mosquito infections were common after feeding on blood from individuals who carry malaria parasites but do not have disease symptoms. It was shown that even though younger age groups experience most of the disease, older children and adults contribute significantly to the reservoir of infection.

“The capacity to infect mosquitoes and the number of opportunities to transmit are the two key determinants of malaria transmission”, said Bronner Gonçalves, an epidemiologist at the LSHTM and co-author of the study. Using these data, the team was able to estimate the contributions of children and adults to malaria transmission in different settings. “Children are more infective to mosquitoes than adults, but receive fewer mosquito bites – this balances their contribution to transmission”, said Melissa Kapulu, who is based at the KEMRI-Wellcome Trust Programme, in Kenya.

Figure adapted from table 3 in Gonçalves et al., 2017.

Understanding this disparity should help with developing more strategic malaria control methods.

$7 million programme funded by the Bill & Melinda Gates Foundation

A new $7 million project, INDIE (P. falciparum infection dynamics and transmission to inform elimination), will build on the work described above and investigate how the infectious reservoir is maintained when different malaria control methods are used.

Chris Drakeley, who will lead this new programme, said, “our aim is to identify the individuals who are infecting mosquitoes when standard and more targeted control measures are in place”. Teun Bousema, the co-lead of this programme, added, “this project will generate unique data that will be used by malaria control programmes to more efficiently interrupt parasite circulation and guide the last steps towards malaria elimination”.